Thermal transfer printing processes utilize a heat-activated pigmented material which is transported on a thin polymer foil. The pigmented material is brought into contact with a receptor material, commonly a vinyl, paper or other receptor material, and heat and pressure are applied to the reverse side of the foil, causing the pigmented material to bond to the receptor material. When the foil is pulled from the receptor material, the pigmented material is released from the foil.
Heat is supplied by electric heating elements mounted in a linear array on a thermal print head. Each of these heating elements is individually controlled by a computer to heat up or to be allowed to cool down. In one application, the density of the heating elements is 300 per inch along the print head.
The receptor material and the foil are passed together under the print head, which presses the latter down on the former. At controlled intervals, the heating elements are caused to heat up and transfer pigmented material from the foil to the receptor material in controlled patterns defining a printed image. As the foil and receptor material emerge from beneath the print head, the foil is separated from the receptor material, leaving the printed image on the receptor material.
One example of a printing apparatus employing this process is shown in U.S. Pat. No. 5,537,135 and is sold by Gerber Scientific Products, Inc. under the trademark GERBER EDGE. The present invention is particularly suited for use with this printing apparatus.
If any foreign material is present between the foil and the receptor material, the transfer of pigmented material can be prevented or interrupted, resulting in a void or flaw in the printed image. These flaws, generally caused by flecks of dust or dirt, although quite small in size, are nevertheless noticeable and objectionable, particularly in large, solid color portions of an image.
It is a primary object of the present invention to provide a method and apparatus for the repair of voids or flaws in images printed by the thermal transfer printing process.
It is a further object to provide a repair method and apparatus which is convenient, inexpensive and does not necessitate the maintenance of an inventory of pigmented materials of various colors.
It is still a further object to provide a printing tool for the creation of small images from thermal transfers.